Income Taxes - Total Balance of Unrecognized Gross Tax Benefits Resulting from R&D Credits Claimed (Detail) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 1,041	$ 777	$ 551
Additions (reductions) based on current year tax positions	483	264	226
Unrecognized tax benefits at end of year	$ 1,524	$ 1,041	$ 777

Amount of unrecognized tax benefits pertaining to uncertain tax positions taken in tax returns.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 15A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Unrecognized Tax Benefit
-URI http://asc.fasb.org/extlink&oid=6527854

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant